1. Statement of the Technical Field
The present invention relates to radio frequency identification (“RFID”) devices and more particularly to a system and method for monitoring the relative directional movement and speed of an article within an RFID interrogation zone by use of Doppler detection circuitry incorporated within an RFID surveillance system.
2. Description of the Related Art
Radio frequency identification (RFID) is a term used to describe technologies that use radio waves to automatically identify objects or people. RFID systems may be used for a number of applications such as managing inventory, electronic access control, security systems, automatic identification of cars on toll roads, and electronic article surveillance (“EAS”). This may be done in several ways, the most popular involves storing a serial number that identifies an object or a person, and perhaps other information, on a microchip in communication with a transponder, commonly referred to as an RFID marker or RFID tag. RFID systems may be used to track or monitor the location and/or status of articles or items to which an RFID marker is applied. An antenna, sometimes packaged with a transceiver and decoder, enables the marker to transmit the identification information to the transceiver, which includes the ability to receive and convert the radio waves reflected back from the RFID marker into digital information that can then be passed on to computers for processing. The transmitting antenna, the transceiver and the decoder are often collectively referred to as the RFID reader.
The RFID reader, which can be either a handheld or a fixed-mount device, emits radio waves in ranges of anywhere from one inch to 100 feet or more, depending upon its power output and the radio frequency used. When an RFID marker passes within the antenna's electromagnetic zone, it detects the reader's activation signal. The reader then decodes the data encoded in the tag's integrated circuit and the data is passed to a computer for processing.
While RFID systems provide fast and accurate identification of items to which are applied RFID markers, present RFID systems fail to track the movement and speed of movement of items within the antenna's electromagnetic zone. Thus, when an RFID reader receives item identification information from an interrogated marker it ignores other signals, e.g., Doppler signals, that would indicate the relative motion, direction of motion, and speed of an item. This is due to the fact that the RFID readers either do not include the necessary hardware or logic to detect movement or simply filter out or ignore Doppler signals. Separate Doppler signal detectors often need to be incorporated into the RFID system resulting in an increase of cost, labor and design. Passive Infrared (“PIR”) detectors are often used to detect motion. However, the incorporation of PIR detectors into an existing RFID system requires additional hardware and additional start up costs, resulting in a system that is often impractical.
Therefore, what is needed is a method and system that utilizes existing RFID hardware to detect incoming Doppler signals from an item within the RFID interrogation zone and determines the relative speed and motion of the item.